The present invention is generally related to an optical module. More specifically, the present invention is directed to a structure of a multi-wavelength optical transmitter module which optically multiplexes a plurality of laser light having a plurality of wavelengths with each other and then transmits the multiplexed laser light, and also, directed to a structure of an optical receiver module which optically demultiplexes such a light whose plural wavelengths have been multiplexed so as to receive the demultiplexed light.
Semiconductor laser diode (LD) elements have been utilized in various sorts of technical fields such as information and telecommunication fields as compact light sources operable in higher efficiencies. Very recently, there are strong needs of technical ideas capable of providing laser diode light sources having a plurality of light emission wavelengths as compact light source mounted modules. Conventionally, the above-described technical needs have been made as light sources for wavelength multiplexing communications which employ light having plural wavelengths in optical communication fields. In addition thereto, LDs (laser diodes) of blue color series have been currently developed, and oscillatable wavelengths could be widened in blue color LDs. As a result, as reading/writing light sources of displays and optical disks, higher requirements for multi-wavelengths light source modules have been made even in wavelength ranges of visible light.
As one of application examples of the multi-wavelengths light source modules, there are light sources of laser projectors. Generally speaking, projectors imply such image display apparatuses which project images on screens, and the like, in response to image signals derived from various types of image supplying apparatuses (for example, computers etc.) so as to display the projected images. In general, as conventional projectors, the below-mentioned types of projectors are known, which have mainly employed transmission type liquid crystal panels, reflection type liquid crystal panels, or digital micromirror devices. On the other hand, laser projectors have been designed in such a system that while laser light is employed as light of light sources thereof, the laser light is scanned along a two-dimensional direction so as to display images. As a consequence, these laser projectors can be made compact, and can produce images having superior color reproduction, as compared with those as to the above-described other types of projectors. Conventionally, use places of projectors have been relatively limited only to, for example, meeting rooms, presentation rooms, living rooms of homes, and the like. However, since portable computers have been made compact and portable telephones equipped with higher functions have been marketed in the present stage, qualities and quantities of data which are portable for respective persons are considerably increased, so that these computers and portable telephones can be operated without restricting use places thereof. For example, there are some expectations as to development of ultracompact type projectors operable under low power consumption, which can be assembled in portable computers and portable telephones. As technical ideas related to laser projectors, for example, JP-A-2002-214705 has disclosed the below-mentioned color laser projector: That is, in this color laser projector, 3 sets of light emitted from 3 pieces of laser light sources having different light emission colors are scanned in the two-dimensional direction by optical scanning means which are different from each other, and then, 3 sets of the two-dimensionally scanned laser light are collected to each other in a synchronization manner so as to project color images. However, the color laser projector described in JP-A-2002-214705 has such a problem that since the plural sets of optical scanning means are required, whose total number is equal to that of the laser light sources, there is a limitation when the color laser projector is made compact.
Also, another technical idea has been proposed. That is, JP-A-2006-186243 has disclosed such a color laser projector that R (red), G (green), and B (blue) semiconductor LD (laser diodes) elements which are employed in light sources are stored in one package in order to improve compactness of the light sources and of optical systems thereof. However, in the color laser projector of the above-described JP-A-2006-186243, the light source are merely mounted in the proximity to each other, and three sets of the color laser light are not multiplexed with each other. As a result, the optical axes of the R, G, B laser diode elements are not coincident with each other. Under such a circumstance, in order to secure predetermined resolution, optical systems designed for respective wavelengths of the R, G, B semiconductor LD elements must be separately prepared. Otherwise, if a general technical idea is utilized in order to make the optical axes coincident with each other, then such an optical system as a dichroic prism and the like is required. Even if any of the above-described solving ideas is employed, there are certain limitations when a total number of optical components is reduced, and the optical systems are made compact.